Field of the Invention
The present invention relates to an electrostatic capacitive touch panel device, and an image display device including the electrostatic capacitive touch panel device.
Description of the Background Art
A touch panel device that detects a touch of a pointer such as a finger and determines coordinates indicating a position of the touch (touch coordinates) is widely used in various information processing devices. Particularly, a touch panel device in which a touch panel is mounted on a screen of a display device is widespread as a new user interface of information processing devices.
In a projection-type electrostatic capacitive system being one of electrostatic capacitive systems, a detection circuit detects slight change in touch sensors provided in a touch panel, which is caused by electrostatic capacitance of a human finger. Then, based on such detection results, positional coordinates in the touch panel are calculated. According to this method, a touch can be detected even in a case where a front surface side of the touch panel with built-in touch sensors is covered by a protective plate such as a glass substrate having a thickness of approximately several millimeters.
A projected capacitive touch screen device has advantages such as excellent robustness owing to capability of arranging the protective plate in a front surface, capability of detecting a touch even when gloves are worn, and a long life owing to absence of movable parts. The protective plate of the projected capacitive touch screen device is formed of a transparent resin substrate such as acryl and polycarbonate, a glass substrate, or the like. In a case where such a structure is used that an outer profile size of a touch surface to which positional information is input with a pointer such as a finger is made larger than a sensor surface for detecting electrostatic capacitance so as to have the sensor surface overhung and covered by the touch surface, a product excellent in design can be provided (refer to Japanese Patent Application Laid-Open No. 2016-224728).
In such a touch panel device, a surface to be operated by a pointer such as a finger is made of glass or the like, thereby securing durability, and is therefore often used under a condition where a high dielectric substance, such as rain, sea water, beverage, and chemicals, adheres thereto. Robustness is required as an ability of the projected capacitive touch screen device, and stable operation without misdetection even at the time of moisture adhesion is required in addition to capability of highly sensitive detection even when gloves are worn and the like.
For example, Japanese Patent Application Laid-Open No. 2013-222283 discloses a touch panel device that suppresses misdetection even in a case of adhesion of a water droplet or the like.
In a structure of a projected capacitive touch screen device, a touch panel substrate with built-in touch sensors and a protective plate are often attached with a transparent adhesive material (optical clear adhesive (also generally abbreviated as OCA)). As the transparent adhesive material, a material having relative permittivity of approximately from 3 to 6 and water vapor permeability of approximately from 50 g/m2·24 hr to 300 g/m2·24 hr, such as an acrylic resin, is generally used.
Relative permittivity of the transparent adhesive material is changed depending on a temperature, and may be reduced by up to 40% with respect to a room temperature state under an environment of a low temperature (−30° C.) or a high temperature (70° C.). Further, relative permittivity of the transparent adhesive material may be changed through moisture absorption. Such change in relative permittivity is a cause of changing electrostatic capacitance measured by touch sensors.
Further, moisture to be absorbed by the transparent adhesive material enters through a portion exposed to outside air, which is not covered by a protective glass (protective plate) or a touch sensor panel. Therefore, influence thereof is demonstrated as change from a peripheral portion of the transparent adhesive material, which leads to distribution of relative permittivity in a surface of the transparent adhesive material. Thus, the change in relative permittivity of the transparent adhesive material not only influences self-capacitance and mutual capacitance of a touch region of a touch panel, but also tends to influence a peripheral portion of a surface of the touch panel. Thus, lead-out wiring of the touch sensor panel that is wired along a periphery of the touch sensor panel is also subjected to such influence.
Particularly, in a highly sensitive touch panel device that is adaptable to use of gloves and the like, electrostatic capacitance formed by a pointer is extremely small, and hence, relatively, influence due to change in relative permittivity of the transparent adhesive material becomes larger. A touch panel device disclosed in Japanese Patent Application Laid-Open No. 2016-224728 suppresses change in electrostatic capacitance coupling between touch sensors and a conductor such as a metallic frame of a display device at the time when a substance having extremely high relative permittivity (relative permittivity of approximately 80), such as water, adheres to a protective glass, to thereby suppress misdetection of a touch panel.
However, as means of suppressing change in electrostatic capacitance coupling, a protective glass having a black frame printing that is formed of conductive electrodes and a circuit for driving the conductive electrodes are required, which leaves a problem in increase in cost for components. Further, influence of moisture absorption of the transparent adhesive material is not particularly taken into consideration.